While presbyopia is not a devastating opthalmological problem, it is the ony ocular affliction which affects all individuals at the prime of their productive lives. Despite this, there is very little research being done on its etiology, probably because until not there were no known animal models for presbyopia and because it has been regarded as an inevitable affliction which develops with mathematical certainty. However, this dogma is based on a study which would not meet current biostatistical standards. Recently, it has been shown that the rhesus monkey may serve as an excellent model for human presbyopia: the accommodative amplitude in this species decreases from a remarkable 30-40 diopters in one-year-olds to almost zero by the age of 31. The long-term goal of this project is to elucidate, using the rhesus monkey and possibly other suitable animal models, the mechanisms which result in a continuous decrease in the accommodative amplitude; to isolate the biological and/or environmental factors which affect the rate of this decrease and, hence, determine the onset of presbyopia; and to find means to forestall its onset. Our specific aims for the 5-year period are: to define the natural history and the time-course of development of presbyopia; and to describe the lenticular, zonular, and ciliary mechansims which are involved in normal accommodation and contribute to the age-dependent decline in accomodative amplitude. Basic information (refractive power and axial dimensions of the resting and accommodated eye, corneal curvature, etc). will be collected over a 5-year period on populations of caged rhesus at the Wisconsin Regional Primate Center (available age range: 0.5-31 years), and free-ranging rhesus (available age range: 1-20 years) at the Carribean Primate Research Center, P.R. More detailed slit-lamp photomicroscopic and dynamic refraction studies will be done on iridectomizes rhesus and/or cynomolgus eyes. Invasive experiments will also be done to identify factors which stimulate continuous lenticular growth or may in other ways contribute to the continuing decrease in accommodative amplitude. A better understanding of the biological and environmental factors which determine the rate of accomodative loss is a prerequisite for the acceptance of the inevitability of presbyopia or for finding some practical means to forestall the onset of this affliction.